The invention relates to a concentrating solar receiver and more particularly to a solar receiver of the type which may remain in a fixed orientation relative to a portion of the sky. That is, the receiver does not necessarily track the sun continuously through the day although the receiver or group of receivers may be moved during the solar day if it is required by receiver geometry. Periodic adjustments are usually made during the solar year to compensate for changes in the relative path of the sun across the sky, e.g., summer and winter solstice and equinox.
The receiver is adapted to produce electrical and/or thermal energy from resultant exposure to solar radiation. The receiver, in a preferred form, has as a major component a blown glass envelope formed in a manner similar to a light bulb manufacture. The envelope has a concentrating mirror and a photosensitive element or solar cell and/or a heat absorber disposed in a focal zone for the said concentrating mirror.
The invention provides for concentration of sunlight onto the solar cell of appropriate kind (silicon, CdS, etc.) thereby increasing its output. The cell is preferably encapsulated within the envelope. Thermal and electrical energy is removed by appropriate energy conductors.
Previous attempts to produce solar receivers capable of producing electrical power have been hampered by the high cost of photocells and complex technology necessary to manufacture the cells. New techniques however have been developed for producing photocells (e.g., edge defined film growth, dendritic growth, rolled silicon or sheets of cast silica that are recrystallized through heat or molten zones). See for example the publication Proceedings of the ERDA Semiannual Solar Photovoltaic Program review NTIS #Conf. 760837-PZ illustrating such techniques.
The solar cell has been adapted for use in outer space and is effective notwithstanding its rather low efficiency. The use of such devices in space is justified since they are ideally suited for the application. However, their use in domestic solar energy application requires greater utilization (i.e., higher efficiency, per square foot of cell material used and lower cost for each cell). Newer cells, particularly those produced of GaAs exhibit higher efficiency (in the order of 20%) which may offset its higher cost. Concentration of solar energy on the cell increases its output which in turn reduces the effective cost per square foot.
In order to be most effective a solar cell must be cooled. The lower the temperature the more efficient the production of electrical output. In space, radiation cooling is effective to protect the cell. Terrestrial use, on the other hand, is well served by capturing heat produced in the cell for secondary thermal production. Such applications known as hybrid systems produce thermal as well as electrical energy.
In a preferred embodiment the cell is encapsulated in a glass envelope, although it is envisioned that a cell external of the envelope may be appropriately bonded thereto. The glass envelope will protect the cell from the ambient. The envelope should be provided with a reflector surface, which is effective to multiply the effective area of the cell by the concentration ratio of the envelope including the reflector surface.
Variations of the invention and its hybrid application to electrical and thermal energy production will be discussed in the description of the various embodiments.